HETEROPHROSYNID.^. 55 



as local varieties. The Rissoa rubra of INIacgillivray is 

 certainly the present species^ and not Barleeia rubra as 

 he supposed. 



Family X. HE'TEROPHROSY'NID^, Clark. 



Body spiral : mantle plain-edged : head snout-shaped : ten- 

 tacles cylindrical and short, with rounded tips : eyes sessile, or 

 nearly so : foot double-edged in front ; hinder part of the sole 

 slightly grooved down the middle. 



Shell small, conical, and spiral : operculum not spiral but 

 increasing by concentric layers, with the nucleus on the inner 

 side, next to the jjillar ; that side is strengthened by a rib, and 

 furnished underneath with a spike-like process or plate, which 

 projects from the nucleus. 



As the name imports_, these mollusks are abnormal^ 

 allied to the Littorinidce, and distinguishable from that 

 family not much more than the Turbinidae are from the 

 Trochidce^. The operculum is very peculiar. It has 

 an excentric nucleus^ like that of Buccinum, and an in- 

 ternal process analogous to that of Neritina. 



Although the appellation given by Mr. Clark is a 

 long one^ it must in justice and on other grounds be 

 preferred to either of those subsequently proposed by 

 Dr. Gray, viz. Rissoellidte and Barleeiadae. In the sys- 

 tem of the latter author these families are separated 

 by Cuaplidce and several others. 



The Heterophrosynidce are not restricted to the At- 

 lantic Ocean : Dr. P. Carpenter has described some from 

 the Pacific. They inhabit the laminarian zone, and ap- 

 pear to be gregarious. 



* See vol. iii. p. 337. 



